I don't mean this as something for you pros, of course, but has anybody tried putting some sort of tactile markings on the underside of the neck for beginning students? I'm just an amateur and I don't practice four hours a day, so drifting away from correct fingering on the neck of my fretless upright has always been an intonation problem for me. Seems to me that tactile markers for the left thumb might be more legitimate than visual marks on the side of the neck for the fingers. The idea, of course, is just to provide a more consistent base for the "claw," not to dictate where each finger should go down. The tactile thumb markers I've tried are light and do not inhibit the thumb from smoothly sliding up and down the neck. Anybody heard of anyone trying this sort of thing?